1. Field of the Invention
This invention relates to compositions suitable for preparing silicone rubber sponge. More particularly this invention relates to organosiloxane compositions that can be cured by heating to produce a silicone rubber sponge having a uniform, microfine cell structure.
2. Background Information
Silicone rubber sponge is prepared by the addition of an organic blowing agent to a curable organosiloxane composition containing a high consistency organopolysiloxane and a curing agent for the organopolysiloxane. The method used to cure the composition is matched to the decomposition rate of the blowing agent, which is equivalent to the foaming rate for the composition.
Examples of available curing methods for preparing silicone rubber sponge from high consistency organosiloxane compositions include use of organic peroxides and curing by a hydrosilylation reaction employing an organohydrogenpolysiloxane as the curing agent and a platinum compound as the curing catalyst.
Organic peroxides typically require long heating periods to achieve curing, making it very difficult to obtain silicone rubber sponge having uniform and microfine cells. In addition, satisfactory curing cannot be obtained using organic peroxides when the curable composition contains electrically conductive carbon black, which essentially precludes the manufacture of electrically conductive silicone rubber sponge.
A disadvantage of curing organosiloxane compositions using platinum-containing catalysts is the short working time resulting from the high activity of these catalysts. In particular, it is difficult to maintain a balance between the cure rate and the foaming rate of the curable composition. Manufacture of silicone rubber sponge having a uniform and microfine cellular structure by this method is therefore problematic.
The present inventors carried out extensive investigations in order to solve the aforementioned problems and developed the present invention as a result.
One objective of the present invention to provide high consistency organosiloxane compositions capable of being thermally cured to form a silicone rubber sponge exhibiting a microfine and uniform cell structure.